The goal of this study is to define the function of metabotropic glutamate and GABA receptors in the communication link between bipolar and ganglion cells. Recent studies have described and identified several types of metabotropic glutamate and GABA receptors on retinal ganglion cells. The investigator has found that these receptors also modulate bipolar cell transmitter release. The proposed research addresses the mechanisms and the ramifications of their actions on the light response properties of the IPL. One aim will be to determine if bipolar cell transmitter release is controlled by two metabotropic GABA receptor subtypes, one activated by baclofen and the other by cis-aminocrotonic acid. These receptors may regulate different aspects of bipolar cell transmitter release and act under different states of retinal adaptation. Metabotropic glutamate receptors may function as negative-feedback autoreceptors that monitor bipolar cell transmitter release. Subtypes of metabotropic glutamate receptors, localized to each side of the bipolar cell dyad synapse, may differentially modulate transmitter output to amacrine and ganglion cells. Amacrine cells possess both metabotropic GABA and glutamate receptors. The function of these receptors, both as presynaptic autoreceptors and postsynaptic receptors, will be investigated, which will extend our knowledge of synaptic signaling and information processing in the retina.